i personally think that theres nothing wrong with it so far. by the look of things he is trying to get to the same place everyone else is. ie being a perfect jiu jitsu fighter, but he is going down a slightly different path. you wont get to black belt by only knowing two subs nor will you get there knowing a hundred subs that never work. im definitly a ver general fighter when i roll, but im trying really hard to become specific and only focus on a couple of subs. if you can sub anyone with a move then imo you can roll a lot more relaxed because you know that you always have a hidden weapon ready to use. its like in mma when a guy is so good on the ground, he can let his hands go and do things others might not because he doesnt mind going to the ground.
aside from that, if he is killing in comps then good on him.
the problem will be if thats all he is does. if he never looks to learn any other move and get it up to that level or even if he only ever learns one or two ways into the sub then he will reach point where people will defend better than he attacks. hopefully when he gets there he will move on to something else.
bruce lee said (atleast something like) "I do not fear the man who has practised 1000 kicks once, i fear the man who has practised one kick 1000 times"
i just hope he doesnt get bored and quit. if a guy is doing well enough to beat all these people then he might make something out of himself with it.
and my last worry is that he is using a bit of technique but does he use a lot of strength as well, cos that could point to him that he doesnt have as much technique there as you might think. when he gets iit on a brown or black belt his size, then u know its definitly legit